OmniGraffle is a diagramming and digital illustration application for macOS and iOS.

Lovely Charts is an online diagramming application that allows you to create professional looking diagrams, such as flowcharts, sitemaps, organisation charts,…

Grafio is a fun and capable diagraming app for iOS with plenty of features at a fraction of the cost of others.

Storyboard That is a free online storyboard creator.